Inadvertent needle stick injuries from used syringes may present a significant health hazard to others if infectious blood products are transmitted. Such accidental needle sticks may spread hepatitis, AIDS and other communicable diseases to health care workers and patients. In certain instances, the resulting disease may be life threatening. Further, the emotional distress from the fear of contracting such diseases can be significant. Still further, in the event of a stick, series of diagnostic blood tests may have to be performed to determine if cross-contamination has occurred in a needle stick injury. In many cases, the victim often is required to receive injections of gamma globulin to prevent further infection and to cure the patient. This is uncomfortable, inconvenient, and expensive to the victim.
According to the prior art, the usual technique has been to, after use of the needle, to break off the needle and dispose of the needle and syringe in a “sharps” container for secured disposal such as by incineration or stabilization in, for example, plastic of concrete.
Efforts have been made to develop syringes which attempt to prevent inadvertent sticks. In Chen, U.S. Pat. No. 6,432,082 issued Aug. 13, 2002, there is disclosed a safety syringe having a needle holder which is retractable into the barrel of the syringe. The needle holder is secured to the syringe barrel by a frangible component. After use, the uses forces the plunger to couple with the needle holder and withdraws the plunger to rupture the frangible component so that the portion of the holder mounting the needle (cannula) can be withdrawn into the barrel. A drawback of this design is that the frangible portion of membrane must be manufactured to tolerances such that (1) the pressure imposed by the plunger during aspiration of the medicine into or injection of the medicine out of the syringe does not rupture the seal and (2) still provide for rupturing the portion during withdrawal of the plunger without the plunger first separating from the needle holder. It is submitted that such requirements contribute to the expense of such a device. Further, the inability of the health card provider to rupture the portion will cause frustration and abandonment of the operation to withdraw the needle.
In Jenson, U.S. Pat. No. 5,540,660 issued Jul. 30, 1996 there is disclosed another syringe where a needle holder is captured by the plunger for withdrawal into the syringe barrel. In one embodiment of this disclosure, the plunger makes and interference fit into a tapered sleeve such that withdrawal of the plunger withdraws the sleeve and needle into the barrel. A drawback of this arrangement is that it would be difficult to aspirate medicine into the syringe without creating an interference fit between the plunger and sleeve thus disabling the syringe before injection of the medicine. In another embodiment an snap connection is utilized to couple the plunger to a needle holder. In either embodiment, close tolerances must be adhered to during manufacture to provide the seal between the sleeve and needle holder. Further, for either embodiment, an arcuate cannula is required to prevent re-use of the device.
Mazur, U.S. Pat. No. 5,205,824 issued Apr. 27, 1993 discloses another syringe where the needle holder is retained at the end of the syringe barrel only by the friction between the o-rings and the barrel which, it is believed, would (1) make secure attachment of the needle to the holder difficult since the holder may tend to rotate as the needle is threaded thereon. Further there remains a risk that insertion of he needle into a bottle of medicine for aspiration of medicine into the syringe would dislodge the needle holder and interfere with the seal.
There is a need for a safety syringe which is easy and inexpensive to manufacture, which provides for withdrawal of the needle into the barrel of the syringe, which can be re-used if desired, which has a positive coupling to provide for attachment of the needle and retention of the needle during aspiration and injection, which provides for a positive stop during withdrawal of the needle to indicate full withdrawal of the needle and which overcomes the drawbacks noted above.